Some works take place in a world that is just like the real world, and some take place in a world that clearly isn't. These works start out in the real world but then very definitely leave it. Sometimes, it's because fantastical or science-fiction elements are introduced into a work that up until then had been "real world". Sometimes, the setting is revealed to have an Alternate History that distances it from reality.
These new elements might bring about a Genre Shift if they change the focus of the work enough. Conversely, a Bizarro Episode, Paranormal Episode, Cryptid Episode or Alien Episode might take a brief vacation from reality, but doesn't affect the series' continuity.
Compare and contrast the Masquerade, which hides the fantastical elements of the setting from Muggles (but not necessarily the viewer), and The Unmasqued World, when the Masquerade breaks down. See also Mundane Fantastic when the viewer is surprised by the reveal but characters see it as normal, Denser and Wackier, where the work gets crazier as it goes on, Later Installment Weirdness, where later story elements, format, and/or tone deviate from those of the earlier parts of a series, and Earth Drift, where the series starts off in the real world but then elements are introduced that makes it taking place in the real world not possible.
- Samurai Flamenco starts as a series about a street vigilante who is a model by day and fights crime (mainly public smoking and littering) at night, inspired by his love for Toku heroes. After the infamous Episode 7, where a drug addict turns into a gorilla-like monster, and King Torture reveals the existence of his evil organization, the fantastic elements quickly take over the setting.
- Superhero comics in general. At the very beginning of The Golden Age of Comic Books, they pretty much just fought average crooks, gangsters or (given the period) German/Japanese spies; even characters like Superman often began as the only supernatural elements in an otherwise normal world. The fantasy and sci-fi elements took over pretty quickly, though.
- Alejandro Jodorowsky and Milo Manara's comic Borgia starts as a historical work, albeit one that takes the more sensationalist aspects of the Borgias' lives as fact (notably Lucrezia's incestuous relationships) and, given the artist, large amounts of Explicit Content. At the end, Cesare Borgia is leading a mercenary army equipped with Leonardo da Vinci's inventions, including an air force made of his flying machines.
- Candorville was originally a combination of Anvilicious political gags and Slice of Life stories, many of which revolved the main character and his annoying baby-mama, Roxanne. Then it turns out that Roxanne is an evil vampire who might be destined to rule the Earth. Since then the comic keeps switching back and forth between urban humor and Urban Fantasy.
- The Fast and the Furious started out as a grounded crime drama where the only intense action the film had was the street racing scenes. The moment Dwayne "The Rock" Johnson is introduced is when the movie became the over-the-top popcorn action franchise it's currently known for.
- Hudson Hawk is realistic up to the point where Eddie and Tommy Five-Tone jump off the building and Eddie ends up falling into a chair in the Mario Brothers' apartment (Tommy ends up back at the bar), with no explanation whatsoever. The movie has a number of reality-defying scenes after that.
- ¡Three Amigos!. While the Amigos are traveling to El Guapo's lair, they camp at night in the desert. They start singing, which attracts several desert animals... who suddenly start singing along! Then as they go to sleep, they bid goodnight to each other, and a tortoise says "Goodnight, Ned." There is nothing prior to this in the movie that couldn't happen in reality (unlikely, yes, but not impossible). After this many weird things start to happen, such as the appearance of the Singing Bush, the summoning of the Invisible Swordsman, and the impossible landing of the biplane in Santo Poco.
- The Dexter book series leaves reality in Dexter in the Dark when Dexter's "Dark Passenger", as he refers to his homicidal urges, is revealed to be a demonic spirit inhabiting his body.
- The Tantei Team KZ Jiken Note series is purely realistic for most of the time — it's an edutainment series for tweens, after all. However, Nanaki, introduced in the twentieth novel, claims he has the ability to see spirits; and since then there have been paranormal subplots for subsequent novels—but the main plot maintains realistic.
- Life of Pi is realistic for the most part, but during the last part, Pi discovers an "island" covered in meerkats, floating in the middle of the Pacific. Then he discovers that the island is one gigantic carnivorous plant. He finds a human tooth from a former victim in its leaves. This is basically Handwaved as "well, who's to say something like this can't exist in the real world?"
- Alias starts off as a relatively cut-and-dry Tuxedo and Martini-style spy drama with some of your usual unrealistic Shoe Phones and Plot Technology, but otherwise realistic. Gradually, over the course of five seasons, the show introduces more and more science fiction elements until eventually you've got prophecies, immortality, city-sized balls of Synthetic Hate Plague (or something), special bees that are incredibly venomous and totally docile, and more.
- Family Matters takes place firmly in the real world in its early seasons, but after Steve Urkel is introduced, has a number of science-fiction plots revolving around his inventions.
- From Dusk Till Dawn starts out with a pair of fugitives hijacking a family's motorhome and taking it to Mexico. Reality abruptly leaves the building when they're drinking in a roadside cantina and night falls, and the cantina workers become vampires.
- The first season of Gilligan's Island has no supernatural elements (save for "Three to Get Ready" which had a gem which could supposedly grant wishes and of course the occasional dream sequence). Then a few elements get into season two: seeds which can grant psychic abilities, a robot, Dr. Balinkoff's mind swapping experiment, and a meteor which accelerates aging. Season three features radioactive vegetables, a voodoo witch doctor, Balinkoff's mind control rings, Gilligan getting magnetized, and a jet pack.
- Person of Interest starts with an idea that could exist today, a computer program that analyzes mass surveillance to predict crime, and slowly evolves to a story of all-out war between two rival AIs.
- Pretty Little Liars is set in the real world, even if some of A's tricks defy belief. Spinoff Ravenswood has overt supernatural elements, and one of its major characters is a psychic with ties to the parent show; most notably, her visions helped her save Alison's life the night she disappeared.
- The Suite Life of Zack and Cody leaves reality when they travel to a parallel dimension in an episode that does not have an All Just a Dream ending. Its sequel series, The Suite Life on Deck, introduces a "Groundhog Day" Loop, a mummy's curse, and other increasingly strange plots that become part of the characters' daily lives. That's not getting into the crossovers with That's So Raven and Wizards of Waverly Place.
- for almost two full games, the Shenmue series hews even closer to real-life than most video games do, aside from Ryo's occasional dreams about a mysterious young woman he's never met before. In the last few minutes of the second game, after he's finally met that same girl, the plot suddenly begins to take a turn for the fantastic, with the Phoenix and Dragon Mirrors apparently having mystical properties, and the girl revealing that Ryo and his quest are apparently part of an ancient prophecy handed down in her village. Word of God is that the long-awaited third installment still emphasizes realism, but that explicitly supernatural elements will be part of the story going forward.
- Saints Row started out as a gang war simulator, got weirder as the series went on, then jumped the rails entirely when the fourth game began with aliens conquering Earth. The fifth game went outright supernatural as Satan himself claimed the protagonist... as his child-in-law.
- The original plan for Bob and George was to present a realistic setting at first, and several months into its run, it would slowly reveal itself as a superhero comic all along. Unfortunately, when the intended Mega Man Sprite Comic filler was wrapped up and the intended real comic began, the author couldn't hold back, and the superhero elements were revealed after only one week of strips.